Sample Question from Current Topics in Clinical Microbiology, presented by MediaLab

Recurrent urinary tract infection: Laboratory Identification

Enterococcus ID

Illustrated in this composite photograph is the gram stain of Enterococcus species (upper), illustrating gram positive cocci arranged in pairs and short chains.
The viridans streptococci generally form gram positive cocci in long chains; the gram-positive cells of S. pneumoniae, on the other hand, may appear similar in gram stain.
In the lower right is shown a 6.5% NaCl tube. The turbidity indicates growth, a unique characteristic for Enterococcus species.
In the lower left frame is a picture of a bile esculin hydrolysis slant, showing a positive reaction (black pigment) characteristic of Enterococcus species. The streptococci are uniformly negative.
Some strains of Leuconostoc species and Pediococcus species can grow in 6.5% NaCl and are bile-esculin positive; however, they should be ruled out because of the negative PYR reaction.

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